In general, construction machinery is provided with front working apparatuses, such as a boom, an arm, and a bucket, and a swing motor for turning an upper body.
A hydraulic pressure device of the construction machinery will be described with reference to accompanying FIG. 1.
As illustrated in FIG. 1, in the hydraulic pressure device of the construction machinery, a hydraulic pump P may be provided as first and second hydraulic pumps P1 and P2, a plurality of control valve units for controlling supply of working fluid to each of the front working apparatuses is disposed in a hydraulic line through which working fluid is discharged from the hydraulic pump P, and bypass cut valve units 16 and 26 are disposed downstream of the control valve units.
A first driving motor control valve unit 10, a boom control valve unit 12, a bucket control valve unit 14, and the like are disposed in the hydraulic line connected to the first hydraulic pump P1, and a first bypass cut valve unit 16 is disposed most downstream.
A second driving motor control valve unit 20, a swing control valve unit 22, an arm control valve unit 24, and the like are disposed in the hydraulic line connected to the second hydraulic pump P2, and a second bypass cut valve unit 26 is disposed most downstream.
The working fluid is discharged to a drain tank 50 via the first and second bypass cut valve units 16 and 26. This is for the purpose of suppressing loss of fuel efficiency due to discharge of the working fluid by the first and second hydraulic pumps by preventing the working fluid from being drained to the drain tank 50 during a normal operation of the construction machinery.
The first and second bypass cut valve units 16 and 26 are maintained in a closed state in a general situation, and are opened when receiving an open instruction.
First and second hydraulic lines 41 and 42 are connected to the swing motor control valve unit 22, and both end portions of the first and second hydraulic lines 41 and 42 are connected to the swing motor 30.
Further, one side of a makeup line 43 is connected to the swing motor 30. The other side of the makeup line 43 is connected to the drain tank 50.
Control (operation) of the hydraulic pressure device in the related art will be described below.
When a turning instruction is given by operating a joystick, a turning signal moves a spool of the swing control valve unit 22 and provides working fluid discharged from the hydraulic pump P to the swing motor 30.
The working fluid is provided to the swing motor 30 through any one of the first hydraulic line 41 and the second hydraulic line 42, and is discharged through the other one. Accordingly, the swing motor 30 is driven to turn the upper body of the construction machinery.
Then, in order to stop the turning of the upper body of the construction machinery, the swing control valve unit 22 is switched to a neutral position by operating the joystick, so that the supply of the working fluid to the swing motor 30 is stopped.
However, since there exists force continuously turning the upper body by inertia, the swing motor 30 cannot be immediately stopped, and is stopped after being temporarily turned a little longer.
As illustrated in FIG. 3, the supply of the working fluid to the swing motor 30 is stopped, so that a cavitation phenomenon is generated in the hydraulic line to which the working fluid is supplied when the swing motor is turned.
More particularly, the amount of makeup fluid is provided through the swing control valve unit 22, and the like by a stop time (t1) of the swing motor 30, but the supply of the working fluid from the hydraulic pump P is stopped after the stop time (t1), so that the makeup fluid is not additionally provided.
However, there is no inflow of the working fluid into the first hydraulic line 41, which is used for supplying the working fluid, and the swing motor 30 is turned by inertia, so that pressure is rapidly decreased. The discharge of the working fluid is blocked in the second hydraulic line 42 which is used for discharging the working fluid, and the swing motor 30 is turned by inertia, so that pressure is temporarily and rapidly increased, and then is decreased.
That is, there are concerns that durability of the hydraulic line at the pressure increasing side is negatively influenced, and the cavitation phenomenon may be generated at the pressure decreasing side.
Accordingly, in order to prevent the cavitation phenomenon, the working fluid is sucked from the drain tank 50 through the makeup line 43 directly connected with the drain tank 50 to supplement the working fluid as illustrated in FIG. 2.
However, it is necessary to secure the amount of fluid through the makeup line 43, but any pressure is not formed in the drain tank 50 by atmospheric pressure, and there is a limitation in absorption force generated by the operation of the swing motor 30, so that it is realistically difficult to secure the amount of fluid for makeup.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.